Articles such as airfoils must be of light weight and have a high resistance to bending. This is accomplished by providing top and bottom surface regions that have high tensile and compression strength and by providing material below the surface that will stabilize the surface regions as by supporting them against column-type collapse when under compression. In addition, the surfaces of the articles generally must be smooth. A light weight article with surfaces that were smooth or of closely controlled surface texture and that was highly resistant to bending, would be of value.
In accordance with one embodiment of the present invention, an article such as an airfoil is provided, which is of light weight and high bending strength, and which has surfaces that are smooth or of closely controlled texture. The article comprises a core part that includes a body of foam and reinforcing layers at the surfaces of the body, with the reinforcing layers having pores or spaces penetrated by foam that is integral with the foam of the body. Upper and lower strengthening layers that include multiple fibers, lie at the top and bottom surfaces of the core part. A plurality of fastener parts such as threads, extend through the strengthening layers and the reinforcing layers of the core part, and preferably through the entire combination of core part and strengthening layers at its opposite surfaces, to hold them together. A resin penetrates the pores or spaces of the strengthening layers and forms a smooth or closely controlled texture surface of the article.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.